Hurricanes are known for their destruction. Whipping winds, fast-flowing floods and soaring storm surge take lives and rack up billions of dollars in damage each year. Devastating as they are to humankind, hurricanes also play a role in creating a balance of energy on Earth, as they transfer heat across the globe.
Earth is inherently unbalanced when it comes to the distribution of energy in the form of heat. Tropical cyclones offer the planet one way to move energy from the tropics to higher latitudes both in the atmosphere and in the ocean, said Kim Wood, a hurricane researcher at the University of Arizona.
“Balance is preferred, and when things are imbalanced, forces come into play to try to regain balance,” Wood said. “Having one spot warm and another spot cold will induce forces to redistribute heat.”
When the sun shines on Earth, lower latitudes receive more direct sunlight than higher latitudes due to the tilt of our planet. Land also heats up faster than water, creating uneven heating between the oceans, continents and the air above them. The temperature differential induces circulation, moving around temperature and moisture. The atmosphere reacts to these movements and, for example, results in the formation of a tropical wave off the coast of Africa, which can then move out over the ocean and potentially become a hurricane.
“We have hurricanes in part because of this uneven heating that occurs and provides these disturbances that are necessary for hurricanes to form,” Wood said.
But it’s not that easy to create a hurricane. Full-fledged hurricanes have a long list of ingredients that need to fit together just right. Spin in the air helps create rotation in the storm. Warm waters help provide energy to the storm. Instability in the environment allows air to keep rising so thunderstorms can persist and strengthen. Consistent winds in the upper and lower atmosphere help keep the hurricane’s core intact. Moisture in the air also helps create storm clouds.
Most of the time, tropical waves don’t end up forming hurricanes, said Wood. “Quite a few of those disturbances just keep chugging along and don’t do much. We see far more sea disturbances then we see resulting hurricanes from those disturbances,” she said.
The path of the storm, though, is less contingent on the strength of the storm, but relies more on what the surrounding atmosphere is doing. Winds, which are also created due to the uneven heating of Earth, steer the storm like a cork in a stream.
As hurricanes travel across the ocean, scientists can measure a change in the heat energy in the water. Strong hurricanes often leave behind a “cold wake,” where sea surface temperatures are much cooler than the surrounding waters. The cooler signature is partly a result of the energy used up by the hurricane, which it used to maintain or intensify itself. The hurricane also churns up cooler, deeper waters, sometimes bringing life deeper in the ocean to the surface.
Storms also redistribute heat through precipitation. Storms take up water from the ocean through evaporation, which is a cooling process on the ocean surface. When rain falls, condensation is a warming process, releasing energy and causing the temperature of the surrounding atmosphere to rise.
“Precipitation is occurring in different places because heat energy is being redistributed,” Wood said. Beyond the heat element, the rain can sometimes ease parched lands, replenish lakes and break up harmful algae blooms.
A hurricane fizzles out when it starts losing its ingredients, such as warm water. It can weaken over land or when it passes over cold water.
No matter where they bend and end, tropical cyclones are nature’s way of rebalancing order on Earth.
This article is part of Hidden Planet, a column that explores wondrous, unexpected and offbeat science of our planet and beyond.
How hurricanes keep Earth's energy in balance – The Washington Post
20 Nov